Time-Resolved EPR Study of Singlet Oxygen in the Gas Phase

Singlet oxygen O2(1g) is an important intermediate in many photochemical and photobiological processes.1 The physical and chemical properties of O2(1g) have been the subject of extensive investigations during the last several decades, cf. e.g., ref. 2 for a review. At least a hundred of publications, numerous review articles, and books are devoted to O2(1g) in the condensed phase. Detection of O2(1g) and monitoring of its reactions in solution are commonly accomplished through observation of the characteristic luminescence of O2(1g) at 1270 nm.

Although O2(1g) does not possess a net electronic spin, it is paramagnetic due to its net electron orbital angular momentum J= 2 (Scheme 1), and is therefore expected to possess an electron paramagnetic resonance spectrum (EPR).